The present invention relates generally to a closure, and particularly to a closure for enclosing one or more elongate objects.
The present invention finds particular utility as a closure for protecting junctions between elongate objects such as pipes or cables. The term xe2x80x9ccablexe2x80x9d will be understood hereinafter to include both conductive cables and bundles of optical fibres. When it is necessary to make connections between elongate objects such as pipes or cables the junction or splice where such objects are joined end-to-end is necessarily less strong and less resistive to environmental agents liable to cause deterioration over time than the cable itself.
In the production of, for example, cable systems such as telecommunication or power transmission systems, it is frequently necessary to make splices either to join cables end-to-end or to make a branch. The cables and the splices may be located underground, in conduits or in other environments, inside or outside buildings, but in any event are always at risk to the ingress of environmental agents such as moisture and humidity or dust. Underground installations are also subject to pressure, and in particular hydrostatic pressure, whilst above-ground installations suffer from diurnal thermal dilatations. In order to provide environmental seals for splices in cables or other elongate objects various protective measures are known. Systems utilising an enclosing casing with a gel or other suitable sealing material enclosed within it have been found to be particularly valuable. One advantage of using closures containing a gel or other such sealing material lies in the fact that they can be installed at room temperature, and by utilising compression means the gel can be maintained in contact with all the interior surfaces of a closure as well as the exterior surfaces of the cable or other elongate object the splice in which is to be protected. The force applied by the compression means must be sufficiently great to overcome any forces which may be exerted by the environmental agents, such as the hydrostatic head in underground installations. The requirement for a compressive force on a sealing material has been recognised for some years and is described in various prior art documents. In particular, U.S. Pat. No. 4,600,261 (Raychem) describes an apparatus and method for protection of electrical contacts in which the apparatus includes a gel, first means to contain the gel, second means to retain the gel within the first means, and a force means which acts on the first means so that the gel is maintained in compressive contact with the electrical contacts and substantially encapsulates the conductive portion of them.
In that document the means for applying the force comprised an external clip or spring by which two halves of a closure casing were held together and pressed into contact with one another by the spring. Although effective this system has the disadvantage that the components must be made to accommodate a particular size (or relatively narrow size range) of elongate objects over which the spring can exert an appropriate force.
In order to ensure the sealing effect cable closures incorporating relatively displaceable end walls displaceable by screw-threaded means were devised, as described in WO 95/15600 (Raychem). A spring interposed between a nut and a displaceable end wall acting effectively as a piston allowed compression to be applied to a sealing material encapsulated within the sealing closure. It was also appreciated that the displacement direction need not be parallel to the length of the elongate objects enclosed within the casing, but could be transverse this direction, and the above prior art document also describes the provision of piston-like members acting perpendicularly to the length of an enclosed cable whereby to place a gel under compression.
Although all of these arrangements act well to provide a secure seal they nevertheless offer only a secure seal over a relatively limited range of cable diameters. In order to be able to provide a secure seal over a relatively large range of diameters of elongate objects such as cables a relatively large range of movement must be available in order to change the volume of the containment closure over a wide range.
The present invention seeks to provide a closure for elongate objects which is capable of accommodating such objects over a relatively wide range of dimensions, preferably up to a 3:1 ratio of diameters, whilst nevertheless offering a secure seal against environmental agencies.
According to one aspect of the present invention a closure casing comprises two casing parts, means for holding the two casing parts together in juxtaposed relationship, and having means for sealing between an elongate article penetrating the casing and the casing itself, the casing parts having respective cavities together forming a sealant chamber for receiving sealant material and through which the elongate article passes in penetrating the closure casing, the volume of the sealant chamber being adjustable whereby to apply a compressive force to sealant material therein, the adjustment being effected by displacement of at least one element located within the said sealant chamber, the said element being displaceable within the chamber by selectively operable positionxe2x80x94adjustment means of the casing whereby to determine the effective volume of the sealant chamber.
According to a second, more general aspect of the present invention there is provided a closure casing having means for sealing a space between an elongate article penetrating the casing and the casing itself, the casing comprising two opposite casing parts having means for holding them together in juxtaposed relationship and each having respective cavities together forming a sealant chamber for receiving sealant material and through which the elongate article passes in penetrating the closure casing, and means for applying a compressive force to the sealant material transversely of the length of the elongate article whereby to urge it into intimate contact with the said elongate article to seal thereto, in which the said means for applying a compressive force comprise selectively operable adjustment means for determining displacement of a movable member the position of which determines the effective volume of the said sealant chamber.
In one embodiment of the present invention the said displaceable element comprises a plunger guided for movement within the said sealant chamber in a direction substantially transverse the length of the said elongate article. Preferably there are two relatively displaceable plungers interconnected and guided for substantially rectilinear movement within the said sealant chamber.
The said two plungers may be interconnected by screw threaded adjustment means.
Compression on the sealant may be maintained after adjustment, despite changes in volume due to thermal and other effects if there are provided energy storage means between the adjustable position-determining means and the said at least one displacement element. Such energy storage means may comprise a spring, preferably a compression coil spring.
In a preferred embodiment of the invention the screw threaded adjustment means comprise a threaded shaft having operating means at one end thereof by which the shaft is turnable, and a cooperating threaded hole in one of the said two plungers, the spring acting between the other of the two plungers and the said operating means.
In another aspect the present invention comprises a closure comprising a closure casing having openings for the passage of elongate objects and sealing means including a sealing material enclosed within at least part of the closure casing, in which the sealing means includes a relatively displaceable wall part of the closure joined to the remaining part of the closure by a flexible hinge part, and adjustable position-determining means for determining the relative position of the said relatively displaceable part of the closure and the remaining part thereof whereby to regulate the effective volume of the said part of the closure and thus the pressure on a material contained therein.
Preferably the said flexible hinge part is of corrugated or bellows configuration and extends at least partly around the said relatively displaceable wall part. Alternatively the flexible hinge part may comprise or include ligament hinges between appropriately shaped hinged wall parts. As used in this specification the term xe2x80x9cligament hingexe2x80x9d will be understood to refer to a hinge formed integrally in a body of material such as polypropylene and defined by a line of reduced thickness at which molecular orientation under stress takes place during preliminary flexing.
The said flexible hinge part is, however, preferably formed as a roll seal. The roll seal preferably comprises a flexible wall portion around the periphery of the said relatively displaceable wall part, having a single U-shape cross section. This U-shape cross section may be convex towards the interior or the exterior of the casing although, for reasons which will be explained in more detail below, it is preferred that the roll seal is convex towards the interior of the casing.
In order to obtain the maximum range of variation in the dimensions of the elongate objects which can be sealingly accommodated within the closure it is preferred that the said relatively displaceable wall part of the closure is displaceable transversely of the length direction of the said elongate objects.
Various different means for determining the position of the relatively displaceable wall part may be adopted. Preferably, however, the adjustable position-determining means comprise co-operating screw-threaded components acting to apply a force between the said relatively displaceable wall part of the closure and the remaining part thereof. Alternatively, lever mechanisms, especially toggle mechanisms may be provided for this purpose.
In embodiments in which the adjustable position-determining means are screw-threaded components, there may be further provided energy storage means between the said adjustable position-determining means and the said relatively displaceable wall part of the closure. Conveniently such energy storage means comprise a spring which, in the preferred embodiment is a compression spring, preferably a coil spring.
In one embodiment of the invention the co-operating screw-threaded components comprise a threaded shaft and a nut, one operatively linked to the said relatively displaceable wall part of the closure and the other operatively linked to the remaining part of the closure. Relative rotation between the said threaded shaft and the said nut can be effected by means of a control knob connected to one of them, the dimensions of the control knob being such as to extend over the said flexible hinge part of the closure whereby to protect it from incident ultraviolet radiation. This is particularly convenient if the said flexible hinge is formed as a roll seal as described above since such a seal may comprise relatively thin flexible material which could be degraded over time by UV radiation causing it to harden and therefore crack.
In order to achieve a suitable degree of compression of the sealing material, and in particular to allow accommodation of dimensional variations (both expansion and contraction) due to thermal dilatation, it is preferred that there be provided means for identifying the attainment of a predetermined energy storage state of the said energy storage means. In embodiments in which the energy storage means comprise a compression spring, the said means for identifying the attainment of a predetermined energy storage state may comprise co-operating components on two relatively movable members, which come into interfering relationship with one another when the energy storage means is in the said predetermined energy storage state. Preferably the sealing material comprises a gel. Suitable gel materials have been described in the prior art, and may comprise one which preferably has a cone penetration value from 100 to 350 (10xe2x88x921 mm), more preferably 200-260, especially 230-250, and an ultimate elongation of at least 200%. Cone penetration may be chosen to ensure that the material is able to be deformed around the elongate objects to be sealed avoiding air voids, but without excessive flow or if desired excessive relaxation over time, and the ultimate elongation may be chosen to ensure that on re-entry into the splice case the material is pulled away from the elongate objects, such as conductors, by the separation of two casing halves of the closure. Cone penetration is measured by ASTM D217-68 at 21xc2x0 C. on an undisturbed sample using a standard 1:1 scale cone (cone weight 102.5 g, shaft weight 47.5 g), the penetration being measured after 5 seconds. Elongation is measured by ASTM D638-80 at 21xc2x0 C. using a Type 4 die to cut the sample, and at a speed of 5 cm/minute.
Suitable sealing can be made by gelling curable polyurethane precursor materials in the presence of substantial quantities of mineral oil, a vegetable oil or a plasticizer or a mixture thereof. The amount of plasticizer may be, for example, 30-70% by weight of the total in the case of a plasticizer such as trimellitate, or 60-80% in the case of a mineral or vegetable oil. Mineral and vegetable oils may be mixed, for example in the ratio 0.7-2.4 parts by weight of mineral oil to 1 part by weight of vegetable oil. Other suitable sealing materials may be made by curing reactive silicones with non-reactive, extender, silicones. A further class of materials comprises those formed by extending triblock copolymers, such as styrene-ethylene-butylene-styrene copolymers (for example that sold under the Shell trade mark Kraton) with a mineral oil. These sealing materials are disclosed in U.S. Pat. Nos. 4,634,207 (Debbaut) and 4,716,183 (Gamarra), the disclosures of which are incorporated herein by reference.
Other suitable materials are discussed in detail in International Application published under WO 92/22114 (Raychem) the disclosure of which is incorporated herein by reference.
It is preferred that the gel is injection moulded into two opposite parts of the closure although it may be pre-formed as blocks.